Commodity thermoplastics are electrically non-conductive. Their inherent dielectric constant, .epsilon..sub.r, can not be significantly altered by changing the polymer, hence additives are used to modify the matrix in order to increase the dissipation of static electricity, or, to render the bulk material sufficiently conductive to ground as molded articles made therefrom in order to accept an electrostatically applied coating material. Some approaches pertain to ESD coatings on plastic substrates which do not contain conductivity enhancing additives. As additives for plastics to increase conductivity, there may be mentioned conductive carbon black, and conductive carbon fibers.
The incorporation of fine denier metal fibers, such as steel or carbon graphite fibers into polycarbonate or ABS/polycarbonate thermoplastic matrices is known and provides good conductive properties without significantly detracting from the physical properties of the matrix. Long fiber (&gt;2 mm length) composites of polycarbonate containing an effective amount of dispersed fibers of graphite or stainless steel are known.
Polyvinyl chloride provides an economical extrusion or molding resin for a variety of office equipment housings, profiles and the like, despite the relatively lower HDT. Particulate additives to provide improved ESD for polyvinyl chloride are known. The uniform dispersion of long conductive fibers in PVC presents problems associated with the broad melt transition of PVC, its thermal instability, high melt viscosity and problems associated with wetting out of fibers with PVC. Chopped fibers of length of a millimeter have been directly incorporated into PVC but the articles derived therefrom have poor physical properties, and many fiber ends that have stress concentrating effects. Moreover, the viscosity and relatively narrow thermal processing window for PVC renders it impractical for pultrusion processing, since high temperatures and dwell times have been observed to lead to unacceptable wetting, degradation and discoloration. It would be desirable to provide increased conductivity for PVC without the need to incorporate relatively high amounts of either conductive fillers/additives or short conductive fibers of length of 1 mm or less, so as to retain as much of the physical properties available from PVC without degrading the resin.